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Even if moonlight isn’t streaming through your curtains, the phase of the moon may affect how well you sleep

Science and myth rarely agree, but new research suggests that the lunar cycle could have an effect on the quality of sleep.

The study by researchers at the University of Basel in Switzerland found that even in the absence of moonlight, participants slept less deeply and for shorter periods during the full moon than at other lunar phases. It is a phenomenon already known in other organisms as the “circalunar rhythm”, but has never before been shown in humans.

Christian Cajochen, who was the lead researcher on the study, said: “A lot of people complain about bad sleep during moon stages, or they claim that ‘it was the moon’, and there’s a lot of myth involved. We decided to go back in our old data to see whether we could effectively quantify such an effect.”

Previous research has found no association between the phases of the moon and human physiology or behaviour. “While I’m quite cautious and sceptical about the data myself, I have to say after a proper statistical analysis that, to our surprise, we found something there,” said Cajochen. “There is a circalunar influence.”

The brain pattern, eye movements and hormone secretion of volunteers were studied while they slept. Participants were also asked for subjective assessments of their sleep quality.

The results, published in Current Biology, showed that around the full moon, subjects’ brain activity associated with deep sleep decreased by 30%, they took 5 minutes longer to fall asleep, had 20 minutes less sleep overall and lower levels of melatonin – a hormone known to regulate sleep. These findings correlated with the volunteers’ own perception that sleep quality was poorer during the full moon.

“I think one issue in the past was that they compared a lot of people by mixing different laboratories, different devices, and including data from patients, so the entire thing was not standardised,” Cajochen said. “The advantage here is that we really had a standardised protocol.”

The data was taken from a previous study that was not originally looking at the moon’s influence. Participants were kept in a very controlled environment, with artificial lighting, regulated temperature and no way of checking the time. This ensured that internal body rhythms could be investigated independently of external influences.

“The only disadvantage with such a standardised procedure is that we could only investigate 33 people,” said Cajochen. “What I would like to do in the future is to increase the number of subjects and then to follow up each person through the entire moon cycle.”

But such a study would have problems of its own, he added. “If you’re actually going to tell people you’re investigating the influence of the moon, then you may trigger some expectation or sensitivity in them. Sleep is also a psychological thing, of course.”

If true, the mechanisms responsible for the phenomenon are unknown. Malcolm von Schantz, a molecular neurobiologist at Surrey University, said: “Essentially it could be either two things: the moon itself has a gravitational pull which somehow affects our physiology. I find that very unlikely as the gravitational pull of the moon is fairly weak. It doesn’t cause tides in lakes for example, only in large oceans. In fact, if you’re sitting within 15 inches of the wall right now then the wall has a stronger gravitational pull on you than the moon does. So I don’t think we have a sort of mini-tide in ourselves.

“The alternative is that there is a ‘counter’, a mechanism which keeps track somehow of the phases of the moon.”

Marine animals are already known to follow a circalunar rhythm and some believe it is tightly intertwined with the circadian rhythm – the other internal clock that many organisms, humans included, have which is entrained to the sun. “In worms, at least, there is a crossover between these two clocks,” said Cajochen. “But we are not worms any more.”

Other researchers have wondered why a human circalunar clock should exist in the first place. Michael Hastings, a neuroscientist studying circadian rhythms at Cambridge University, said: “In evolutionary terms, it sounds plausible to me at least. If you were a hunter gatherer, you’d want to be out there on a full moon, not a new moon. It might be that there’s something about suppression of sleep under those circumstances because you should be out hunting.

“I think at best it’s intriguing. There’s a biological plausibility, if we take the hunter gatherer scenario, with regard to the mechanisms … It is such a striking and unexpected finding that replication by other sleep labs is absolutely critical.”

Not everyone is concerned that there were only 33 subjects – von Schantz even said these numbers are “fairly sizeable” for such a study.

“It’s true, the body of negative data on the effects of the moon on a huge number of parameters is fairly impressive,” he added. “It’s entirely conceivable that all those previous studies are correct, but that there is also an effect in a limited number of other parameters, one of them being sleep, for reasons we don’t yet understand.”